Through the field pullout destruction tests on 10 GFRP anti-floating anchors using the fiber bragg grating sensing technology, the bearing capacity and deformation properties of the GFRP anti-floating anchors in decomposed rock foundation are investigated. The test results show that the load-displacement difference curve of the anchor body and anchorage body of the GFRP anchors in the slip failure model is higher than that in the rupture failure model. The load-displacement difference curve of the anchor body and anchorage body with the anchorage length which is close to the critical one rises steadily. Increasing the diameter of the anchor body is beneficial for improving the bearing capacity of anchors, limiting the displacement of the anchor body and reducing their displacement difference. Additionally, the distribution of the axial stress on the cross-section of the anchor body, which decreases along the anchorage length, shows a reversed S form along the direction of anchorage length. The shear stress of the axial interface increases firstly and then decreases along the direction of anchorage length, and it transfers from the first interface to the second interface with an oblique upward direction. Finally, the displacement difference of the anchor body and anchorage body, calculated by the simplified model for the distribution of the shear stress, is similar to that of the GFRP anchors in the slip failure model. The research results may provide the theoretical foundation for the application of GFRP anchors.